I only have two speakers in the boat( port and starboard in front of seats. I did like to add speaker to the rear of the boat or to the hard top.
What kind of preferences do you have ?
Been considering the same. Looking at putting one on each side under the gunnel up in the area toward the front pointing back. Looks like the fussion rectangle speakers will fit perfectly and a Janssen Bluetooth amp under the wheel or in the cabin. The new cape horns come with this setup and they sound pretty good. Just a push button to connect my phone is the only thing that is exposed.